1. Field of the Invention
The present invention relates to compounds of the general formula I ##STR3## where n is 0, 1 or 2, R.sup.1 and R.sup.2 are each hydrogen, unsubstituted or substituted alkyl, cycloalkyl, aralkyl, aryl, acyl, alkoxycarbonyl or aryloxycarbonyl, or together form alkylene or an unsubstituted or substituted benzo ring and Y is a radical of the formula ##STR4## where the rings A, B and C can be further substituted or benzo-fused, R.sup.3 and R.sup.4 are each hydrogen or unsubstituted or substituted alkyl, aralkyl or cycloalkyl, or, together with the nitrogen, form piperidino, pyrrolidion or morpholine, R.sup.5 is hydrogen, unsubstituted or substituted alkyl, cycloalkyl, aralkyl, aryl, acyl, alkoxycarbonyl, aryloxycarbonyl, alkylsulfonyl or arylsulfonyl and R.sup.6 is hydrogen, alkyl or cycloalkyl, and n is preferably 1.
2. Description of the Prior Art
The ring A can be further substituted by, for example, chlorine, brmine, cyano, methyl, ethyl, methoxy, ethoxy or hydroxyl.
Ring B and ring C can each be substituted by, for example, chlorine, bromine, methyl, ethyl, methoxy, ethoxy, acetylamino, propionylamino or a fused benzo ring.
R.sup.1 and R.sup.2 are each hydrogen or, for example, C.sub.1 -C.sub.4 -alkyl, cyclohexyl, cyclopentyl, benzyl, 2-phenylethyl, 4-methylbenzyl, or phenyl which is unsubstituted or substituted by methyl, ethyl, propyl or butyl, or are each acetyl, benzoyl, C.sub.1 -C.sub.12 -alkoxycarbonyl or phenoxycarbonyl, or R.sup.1 and R.sup.2 together form, for example, trimethylene, tetramethylene or ##STR5## where R is hydrogen, C.sub.1 -C.sub.12 -alkyl, cyclopentyl, cyclohexyl, cycloheptyl, nitro, cyano, chlorine, bromine, hydroxyl, C.sub.1 -C.sub.12 -alkoxy, benzyloxy, amino, C.sub.1 -C.sub.4 -dialkylamino or C.sub.1 -C.sub.12 -alkoxycarbonyl and m is 1 or 2.
Specific examples of radicals R, in addition to those stated above, are methyl, ethyl, propyl, butyl, nonyl, methoxy, ethoxy, butoxy, dimethylamino, diethylamino, dibutylamino, methoxycarbonyl, ethoxycarbonyl and butoxycarbonyl.
R.sup.3 and R.sup.4 are hydrogen or, for example, methyl, ethyl, butyl, pentyl, hexyl, octyl, cyclohexyl, 2-phenylethyl, 2-cyanoethyl, 2-hydroxyethyl, 2-acetoxyethyl, allyl, benzyl or 4-butylbenzyl.
Specific examples of R.sup.5 are hydrogen, methyl, ethyl, propyl, butyl, hexyl, heptyl, nonyl, cyclohexyl, benzyl, 4-cyclohexylbenzyl, 4-(4'-butylcyclohexyl)-benzyl, 4-butylbenzyl, phenyl, 4-butylphenyl, acetyl, propionyl, butyryl, benzoyl, 4-cyclohexylbenzoyl, 4-(4'-butylcyclohexyl)-benzoyl, 4-butylbenzoyl, ethoxycarbonyl, phenoxycarbonyl, butylsulfonyl, phenylsulfonyl and 4-methylphenylsulfonyl.
Alkyl radicals R.sup.6 are, for example, hydrogen, methyl, ethyl, butyl or cyclohexyl.
The compounds of the formula I are particularly useful as pleochroic dyes in electro-optical liquid crystal displays of the guest-host type.
Liquid-crystalline materials which contain pleochroic dyes are used in displays. The use according to the invention is based on known principles, which are described in, for example, H. Kelker and R. Hatz, Handbook of Liquid Crystals (1980), page 611 et seq., R. J. Cox, Mol. Cryst. Liq. Cryst. 55 (1979), 51 et seq, and L. Pauls and G. Schwarz, Elektronik 14 (1982), 66 et seq. Further literature which gives a detailed description of the use according to the invention is referred to in the stated publications.
Dyes for liquid crystal mixtures have to meet a number of requirements (cf. for example J. Constant et al., J. Phys. D: Appl. Phys. 11 (1978), 479 et seq., F. Jones and T. J. Reeve, Mol. Cryst. Liq. Cryst. 60 (1980), 99 et seq., EP 43904, EP 55838 and EP 65869). They must not undergo ionization in an electric field, must have a very high molar extinction coefficient .epsilon. and be highly soluble in the liquid crystal matrix used and chemically and, in particular, photochemically stable, and, in order to achieve good contrast in the guest-host displays, must have a degree of order S which is preferably higher than 0.75 in the particular nematic phase.
Dyes which meet these requirements are predominantly those from the class comprising the anthraquinones (cf. for example EP 56492, EP 44893, EP 59036 and EP 54217). To date, the particular disadvantage of azo dyes has been that they are either not sufficiently soluble or not sufficiently light-stable.
Surprisingly, the dyes according to the invention possess a good degree of order coupled with high solubilities and good light-stabilities in the particular liquid crystal matrix.
The preparation of the appropriate 2-(4'-aminophenyl)-triazoles is known, eg. coupling of p-nitroaniline to ethyl acetoacetate (C. Kjellin, Chem. Ber. 30 (1897), 1965), oxidative cyclization with copper(II) chloride in the presence of ammonium chloride (T. L. Gilchrist et al., Adv. in Heterocyclic Chem. 16 (1974), 60), and reduction of the nitro group (H. v. Pechmann et al., Chem. Ber 42 (1909) 659).
The preparation of the appropriate benzotriazoles by oxidative or reductive cyclization of the o-amino- or nitroazo compound is described in U.S. Pat. No. 2,501,188 and J. Cepcianski and J. Majer, Collect. Czech. Chem. Commun. 34 (1969), 72.
The compounds of Examples 1 and 2 are prepared by diazotization of the 2-(4'-aminophenyl)-1,2,3-triazoles with nitrosylsulfuric acid in glacial acetic acid/propionic acid, followed by coupling of the product to the appropriate aniline. In Examples 3-17, coupling to the particular aniline possessing a free NH.sub.2 group is carried out in a similar manner, after which diazotization with nitrosylsulfuric acid in glacial acetic acid/propionic acid is once again carried out and the product is then coupled to the appropriately substituted aniline (in Examples 3-15 and 19-32) or to m-cresol (in Examples 16, 17 and 18). The dyes of Examples 16, 17 and 18 are prepared by alkylation of the phenolic OH group with butyl bromide or the appropriate benzyl bromide in dimethylformamide in the presence of potassium carbonate at 100.degree. C.
The dyes are purified by chromatography over silica gel, using a toluene/ethyl acetate mixture as the mobile phase, and are then recrystallized from toluene. The purity is checked by means of thin-layer chromatography and elemental analysis.
Typical methods of preparation are described in Examples 1 and 10 below. Parts and percentages are by weight, unless stated otherwise.
Particularly important compounds are those of the formula Ia ##STR6## where B is hydrogen, C.sub.1 -C.sub.4 -alkyl, cyclohexyl, C.sub.1 -C.sub.9 -alkoxycarbonyl, nitro or cyano, B.sup.1 and B.sup.2 independently of one another are each hydrogen or methyl, and B.sup.3 and B.sup.4 independently of one another are each hydrogen, C.sub.1 -C.sub.8 -alkyl, benzyl or cyclohexyl, or, together with the nitrogen, form pyrrolidino, piperidino or morpholino.